Heat is not working!!!

My heat has started to fail me on my truck, It blows out cold air. After about 20 minuets of driving is will just all of a sudden start pushing out hot air. Not sure if it is electrical or just the knobs.
I have a 2002 silverado with the dual climate control knobs that go up and down. Thanks

If your temp guage is showing that your thermostat is working properly, then it sounds like your blend doors is sticking & then just popping open & allowing the warm air to finally circulate. These systems are complicated so if you don't understand how it works, I would recommend taking it to someone who knows.

Had this same problem in my 01', I've been noticing the same issues with my buddies trucks. Just do a back flush on your heater core and see if that helps. I've hardly ever seen a temp door on those trucks fail. I did mine last winter and no problems since.

Had this same problem in my 01', I've been noticing the same issues with my buddies trucks. Just do a back flush on your heater core and see if that helps. I've hardly ever seen a temp door on those trucks fail. I did mine last winter and no problems since.